The present invention refers to an apparatus for feeding bulk material, in particular to a rotary feeder of the type including a housing provided with a top inlet and a bottom outlet and accommodating a cellular rotor which includes a plurality of radial vanes or blades fixed on a shaft which is supported in lateral bearing covers.
In a rotary feeder of this type, the vanes of the rotor radially extend from the shaft to the inner wall surface of the housing and are confined in axial direction by circular lateral disk members. Bearing against the peripheral area of the lateral disk members at the end face thereof facing the adjacent bearing cover is a slide ring which is guided for axial displacement in the respective bearing cover in non-rotational manner. The slide ring is made of polytetrafluoroethylene (PTFE) and ensures a sealing of the chambers between the lateral disk members of the rotor and the respective bearing cover against penetration of dusty particles of the bulk material. Further, the slide ring prevents leakage of air through these chambers which would otherwise occur in view of the differential pressure between the inlet side and the outlet side of the rotary feeder.
The slide ring is urged against the lateral disk members by several prestressed helical compression springs which are supported by and uniformly spaced about the circumference of the respective bearing cover. Practice has shown that the frictional conditions and the forces exerted in the area of the sliding surfaces between slide ring and lateral disk member are difficult to predict and to calculate in advance because of their dependency on numerous, partly time-varying parameters such as material of slide ring and laterial disk member, pressure differential between inlet and outlet of the rotary feeder or wear condition of the slide ring. Further, the compression springs causes a local flexure of the slide ring in the contact area with the latter, and increasing wear of the slide ring results in a decreasing prestress of the compression springs and thus in a decrease of the contact pressure of the slide ring against the respective lateral disk member.
US-PS 4,784,298 describes a rotary feeder with rotor vanes which includes a sealing strip unit for sealing the rotor in radial direction. The sealing strips are pressed against the inner wall surface of the housing by a contact pressure which is generated by a central adjusting unit. The shaft of the rotor is hollow and accommodates an axially displaceable adjusting bar which is acted upon by a compression spring and includes at least two axially spaced conical surfaces. Bearing against these conical surfaces are push rods which are guided in respective bores of the rotor vanes and bear with their other end against the sealing strip units to push same radially outwards. Each sealing strip unit is further acted upon by a pushback force which prevents the sealing strip units from being disengaged and counteracts the generated contact pressure. The pullback force is provided by further compression springs which force the sealing strip units back into the guide grooves of the vanes. Thus, the rotor of such a rotary feeder is of comparably complicated structure. In addition, the radial contact pressure decreases with increasing wear of the sealing strips because the prestress of the compression spring acting on the central adjusting unit diminishes with increasing lengthening of the spring.